The present invention relates to visual displays, and more particularly to addressable, reusable, paper-like visual displays, such as xe2x80x9cgyriconxe2x80x9d (or twisting particle) displays or other forms of electronic paper, such as particulate electrophoretic displays, which are available from E-ink Corporation. Specifically, the invention relates to substrates usable as a writing surface for gyricon displays or electronic paper.
A gyricon display, also called a twisting-ball display, rotary ball display, particle display, dipolar particle light valve, etc., offers a technology for making a form of electric paper and other electronically controlled displays. Briefly, a gyricon display is an addressable display made up of a multiplicity of optically anisotropic particles, with each particle being selectively rotatable to present a desired face to an observer. For example, a gyricon display can incorporate xe2x80x9cballsxe2x80x9d where each ball has two distinct hemispheres, one black and the other white, with each hemisphere having a distinct electrical characteristic (e.g., zeta potential with respect to a dielectric fluid) so that the ball is electrically as well as optically anisotropic. The balls are electrically dipolar in the presence of the fluid and are subject to rotation. A ball can be selectively rotated within its respective fluid-filled cavity, for example, by application of an electric field, so as to present either its black or white hemisphere to an observer viewing the surface of the sheet.
A reflective image is formed by the pattern collectively created by individual black and white hemispheres. By the application of an electric field addressable in two dimensions (as by a matrix addressing scheme), the black and white sides of the balls are controlled as the image elements (e.g., pixels or subpixels) of a displayed image. Alternatively, the display may be controlled by shaped electrodes to form one or more fixed images.
The balls are typically embedded in a sheet of optically transparent material, such as an elastomer sheet. A dielectric fluid, such as a dielectric plasticizer, is used to swell the elastomer sheet containing the balls. Through this swelling, the dielectric fluid effectively creates a fluid-filled cavity around each ball. The fluid-filled cavity accommodates the ball and allows the ball to rotate within its respective fluid-filled cavity, yet prevents the ball from migrating within the sheet.
When an electric field is applied to the sheet over a bead, the electrical force on the bead overcomes the frictional adhesion of the bead to the cavity wall and causes the bead to rotate. Once rotation is complete, each bead will remain in a fixed rotational position within its cavity. Thus, even after the electric field is removed, the structures (balls) will stay fixed in position until they are dislodged by another electric field. This bistability of the beads enables the gyricon display to maintain a fixed image without power. The bistability of a gyricon display is beneficial over other types of displays such as a liquid crystal display (LCD) or a light emitting diode (LED) display which consume energy to maintain an image. Gyricon displays are thus particularly useful for displays which will show an image for a prolonged period of time and only periodically have the image changed.
Gyricon displays are not limited to black and white images, as gyricon and other display mediums are known in the art to have incorporated color. Gyricon displays have been developed incorporating either bichromal color, trichromol color, or four quadrant colored balls. Also developed are three or four segmented colored balls, as disclosed in U.S. Pat. No. 6,128,124 ( Silverman, ADDITIVE COLOR ELECTRIC PAPER WITHOUT REGISTRATION OR ALIGNMENT OF INDIVIDUAL ELEMENTS), incorporated by reference herein.
The colored balls can be charged by adsorption of ions from a liquid onto the ball surface. Alternatively, colored balls can be charged by electret formation by injection of an external charge into the surface region of a colored ball, as is disclosed in U.S. Pat. No. 6,072,621 (Kishi, COLOR BALL DISPLAY SYSTEM), incorporated by reference herein.
Like ordinary paper, electric paper preferably can be written on and erased, can be read in ambient light, and can retain imposed information in the absence of an electric field or other external retaining force. Also like ordinary paper, electric paper preferably can be made in the form of a lightweight, flexible, durable sheet that can be folded or rolled into tubular form about any axis and can be conveniently placed into a shirt or coat pocket and then later retrieved, restraightened, and read substantially without loss of information. Yet unlike ordinary paper, electric paper preferably can be used to display full-motion and changing images as well as text. While gyricon displays are particularly useful for displays where real-time imagery is not essential, gyricon displays are adaptable for use in a computer system display screen or a television.
Gyricon display arrangements have typically taken one of three forms: (1) a slurry coat with balls randomly dispersed in a relatively thick film, (2) a monolayer where balls are closely packed in a layer; or (3) a dual layer, where balls are closely packed in a first layer and a second layer of balls is provided to fill in the voids. To create displays which appear brighter with sharper images, gyricon displays should have high light reflectance. One way to improve the reflectance of a monolayer gyricon display is to closely pack the bichromal balls. However, in dual or multiple layer displays, the packing density of the balls may be of little consequence insofar as overall display reflectance is concerned, because balls located farther from the viewing surface of the gyricon display will xe2x80x9cfill in the gapsxe2x80x9d between balls located nearer the viewing surface. So long as the two-dimensional projection of the balls onto the viewing surface at all distances from the viewing surface substantially covers the viewing surface, a high-quality display will be obtained.
In the context of gyricon displays, the xe2x80x9cballsxe2x80x9d are not necessarily perfectly round or hemispherical. Instead of balls, a gyricon display can use substantially cylindrical bichromal particles rotatably disposed in a substrate. The twisting cylinder display has certain advantages over the rotating ball gyricon display because the bichromal elements can achieve a higher packing density. The higher packing density leads to improvements in the brightness of the twisting cylinder display as compared to the rotating ball gyricon display.
One drawback to twisting particle displays (using balls, cylinders, etc.) is that the quality of the image viewed is dependent on the rotatability of the structures within the fluid. In practice, a particle may not rotate completely or not at all, thus only partially exposing the white or black color or a mix therebetween. Incomplete rotation or non-rotation causes a loss in image contrast and color purity. It is therefore desirable to improve the resolution of the image on the display by improving the rotatability of the structures within the fluid.
To achieve still higher packing density, a gyricon display can be constructed without elastomer and without cavities. In such a display, the bichromal balls are placed directly in the dielectric fluid. The balls and the dielectric fluid are then sandwiched between two retaining members (e.g., between the addressing electrodes) with no elastomer substrate.
Substrates usable as a writing surface for Gyricon displays are known in the prior art. EPO 942,405 A2 (Howard et al., xe2x80x9cCHARGE RETENTION ISLANDS FOR ELECTRIC PAPER AND APPLICATIONS THEREOFxe2x80x9d) discloses a pattern of conductive charge retaining islands on the surface of a Gyricon sheet.
In addition to using the present invention with Gyricon displays, the invention can also be used in combination with particulate electrophoretic displays, such as available from E-Ink Corporation, or other electronic paper. A particulate electrophoretic display, such as available from E-Ink Corporation (or electronic ink) comprises transparent xe2x80x9cmicrocapsulesxe2x80x9d filled with a densely colored fluid such as a dark ink. Contained inside the micro capsule shell are hundreds of tiny solid spheres of a different color, such as brilliant white titanium dioxide, each of which has a negative charge. The micro capsules are typically sandwiched between a transparent conductive top electrode and a bottom electrode. The negatively charged titanium dioxide spheres are held against the bottom side of the micro capsule by a positive static electric field. When the particles are held against the bottom side, the white particles are submerged below the viewing surface of the colored dye inside the micro capsules. When the polarity of the electric field is reversed, the micro capsules are repelled by the negative field and are attracted to the transparent top electrode where the particles coat the top side viewing surface of the micro capsule. The coating of the viewing surface suddenly changes from the color of the dark ink to the color of the white spheres. Thus, a particulate electrophoretic display, such as available from E-Ink Corporation does not require the micro capsules to rotate in order to show a change of color, but rather requires migration of the minute particles within the fluid contained in the micro capsule.
The present invention is a micro structured film having a plurality of isolated electrodes usable as a writing surface for a display panel for gyricon displays or electronic paper. The specific geometry of the isolated electrodes is an array of raised mesas having a semiconductive deposition on the top layer. The individual mesa shaped electrodes are individually addressable by a stylus or other electrical stimulus. The display panel has a viewing surface and a backside surface opposing the viewing surface. The display panel contains particles which are responsive to changes in an electric or magnetic field and are optically anisotropic. The conductive electrode film is preferably transparent to visible light.
The electrode film has an array layer and an electrode layer, where the array layer provides a support structure for the electrode layer. The array layer is electrically non conductive and is disposed toward the display panel. The array layer has a fabricated texture, such as a plurality of mesa shaped segments where each mesa shaped segment comprises a top face and side walls extending downward from the top face. The electrode layer is formed of an electrically conductive material and coats the array layer. The electrode layer is exposed for contact by an electrical stimulus, such as a stylus. The electrode layer can be deposited by a sputtering process, wherein the electrode layer is thicker on the top face than on the side walls producing resistive bridges between adjacent top faces. The resistive bridges partially electrically isolate each electrode from the other electrodes in the electrode layer. Thus, each shaped electrode is capable of being individually addressed by a stylus without addressing other electrode segments.